New supply lines via Tajikstan and Uzbekistan mean Islamabad will only be able to push up costs and inconvenience war effort

Lorries waiting to cross into Afghanistan tail back near the town of Tokham after Pakistan shut its border in protest at a US air strike that killed at 24 of its soldiers. Photograph: Khuram Parvez/Reuters

Pakistan's government once had the power to bring Nato's war machine to a shuddering halt through its control of a key route into landlocked Afghanistan. But today it can only aspire to cause inconvenience and slightly push up the cost of a war already running at $120bn a year.

As Washington's relationship with Islamabad soured in recent years, Nato's logistics chiefs tried to break their reliance on Pakistan for getting enough food, fuel and other vital supplies to their troops in Afghanistan.

Such goods used to arrive almost entirely through what is known as the southern distribution network, which runs from Pakistani container ports on the Arabian Sea over road and rail links to the border towns of Tokham and Chaman.

Those two crossing points are currently closed to Nato traffic following the killing of at least 24 Pakistani soldiers in a US air strike on Saturday.

The supply line has also proved vulnerable to attack from insurgents inside Afghanistan, who have attacked convoys, blowing up dozens of fuel tankers at a time and looting goods intended for troops.

In 2008, Pakistani television showed shots of gleeful insurgents driving around in bullet proof Humvees that had literally fallen off the back of a truck. The vehicles had been en route to Afghan security forces.

Many of the lorry drivers currently stuck in Pakistan because of the closed borders have complained that they are vulnerable to Taliban attacks.

Pakistan has used its power to shut down the supply line before. Last year it did so for 10 days after Nato forces mistakenly killed three of its soldiers.

Today, however, only 30% of US supplies and less than half Nato's travel through Pakistan, the result of the opening of the northern distribution network - a far longer, more complicated and expensive route that starts in Europe. Supplies are put on lorries and railways and moved across most of the Eurasian landmass before entering Afghanistan through the former Soviet republics of Uzbekistan and Tajikistan.

Forty percent of US supplies are shipped in from the north, and another 30% are flown in.

The northern route, combined with stockpiling of essential equipment, means Nato operations could continue unaffected for several months, according to a western military official.

The development of the new route relied on Russian blessing. Despite being troubled by the large US presence in central Asia, Moscow concluded it has no interest in a Taliban return to power. Top-ranking US generals including David Petraeus were also obliged to visit the region to court central Asian leaders like Islam Karimov, president of Uzbekistan, whose regime has been repeatedly criticised for human rights abuses, including torture.

The route through Uzbekistan is currently in question, however, after a key bridge near the Afghan border was damaged by an explosion 10 days ago and has been closed since.

Neither the US nor the Uzbeks have commented on the cause of the explosion, although there are fears it could be the work of the Islamic Movement of Uzbekistan, which is allied to the Taliban.